NAME

    Capture::Tiny - Capture STDOUT and STDERR from Perl, XS or external

    programs

VERSION

    version 0.46

SYNOPSIS

      use Capture::Tiny ':all';

      # capture from external command

      ($stdout, $stderr, $exit) = capture {

        system( $cmd, @args );

      };

      # capture from arbitrary code (Perl or external)

      ($stdout, $stderr, @result) = capture {

        # your code here

      };

      # capture partial or merged output

      $stdout = capture_stdout { ... };

      $stderr = capture_stderr { ... };

      $merged = capture_merged { ... };

      # tee output

      ($stdout, $stderr) = tee {

        # your code here

      };

      $stdout = tee_stdout { ... };

      $stderr = tee_stderr { ... };

      $merged = tee_merged { ... };

DESCRIPTION

    Capture::Tiny provides a simple, portable way to capture almost anything

    sent to STDOUT or STDERR, regardless of whether it comes from Perl, from

    XS code or from an external program. Optionally, output can be teed so

    that it is captured while being passed through to the original

    filehandles. Yes, it even works on Windows (usually). Stop guessing

    which of a dozen capturing modules to use in any particular situation

    and just use this one.

USAGE

    The following functions are available. None are exported by default.

  capture

      ($stdout, $stderr, @result) = capture \&cod;;

      $stdout = capture \&cod;;

    The "capture" function takes a code reference and returns what is sent

    to STDOUT and STDERR as well as any return values from the code

    reference. In scalar context, it returns only STDOUT. If no output was

    received for a filehandle, it returns an empty string for that

    filehandle. Regardless of calling context, all output is captured --

    nothing is passed to the existing filehandles.

    It is prototyped to take a subroutine reference as an argument. Thus, it

    can be called in block form:

      ($stdout, $stderr) = capture {

        # your code here ...

      };

    Note that the coderef is evaluated in list context. If you wish to force

    scalar context on the return value, you must use the "scalar" keyword.

      ($stdout, $stderr, $count) = capture {

        my @list = qw/one two three/;

        return scalar @list; # $count will be 3

      };

    Also note that within the coderef, the @_ variable will be empty. So

    don't use arguments from a surrounding subroutine without copying them

    to an array first:

      sub wont_work {

        my ($stdout, $stderr) = capture { do_stuff( @_ ) };    # WRONG

        ...

      }

      sub will_work {

        my @args = @_;

        my ($stdout, $stderr) = capture { do_stuff( @args ) }; # RIGHT

        ...

      }

    Captures are normally done to an anonymous temporary filehandle. To

    capture via a named file (e.g. to externally monitor a long-running

    capture), provide custom filehandles as a trailing list of option pairs:

      my $out_fh = IO::File->new("out.txt", "w+");

      my $err_fh = IO::File->new("out.txt", "w+");

      capture { ... } stdout => $out_fh, stderr => $err_fh;

    The filehandles must be read/write and seekable. Modifying the files or

    filehandles during a capture operation will give unpredictable results.

    Existing IO layers on them may be changed by the capture.

    When called in void context, "capture" saves memory and time by not

    reading back from the capture handles.

  capture_stdout

      ($stdout, @result) = capture_stdout \&cod;;

      $stdout = capture_stdout \&cod;;

    The "capture_stdout" function works just like "capture" except only

    STDOUT is captured. STDERR is not captured.

  capture_stderr

      ($stderr, @result) = capture_stderr \&cod;;

      $stderr = capture_stderr \&cod;;

    The "capture_stderr" function works just like "capture" except only

    STDERR is captured. STDOUT is not captured.

  capture_merged

      ($merged, @result) = capture_merged \&cod;;

      $merged = capture_merged \&cod;;

    The "capture_merged" function works just like "capture" except STDOUT

    and STDERR are merged. (Technically, STDERR is redirected to the same

    capturing handle as STDOUT before executing the function.)

    Caution: STDOUT and STDERR output in the merged result are not

    guaranteed to be properly ordered due to buffering.

  tee

      ($stdout, $stderr, @result) = tee \&cod;;

      $stdout = tee \&cod;;

    The "tee" function works just like "capture", except that output is

    captured as well as passed on to the original STDOUT and STDERR.

    When called in void context, "tee" saves memory and time by not reading

    back from the capture handles, except when the original STDOUT OR STDERR

    were tied or opened to a scalar handle.

  tee_stdout

      ($stdout, @result) = tee_stdout \&cod;;

      $stdout = tee_stdout \&cod;;

    The "tee_stdout" function works just like "tee" except only STDOUT is

    teed. STDERR is not teed (output goes to STDERR as usual).

  tee_stderr

      ($stderr, @result) = tee_stderr \&cod;;

      $stderr = tee_stderr \&cod;;

    The "tee_stderr" function works just like "tee" except only STDERR is

    teed. STDOUT is not teed (output goes to STDOUT as usual).

  tee_merged

      ($merged, @result) = tee_merged \&cod;;

      $merged = tee_merged \&cod;;

    The "tee_merged" function works just like "capture_merged" except that

    output is captured as well as passed on to STDOUT.

    Caution: STDOUT and STDERR output in the merged result are not

    guaranteed to be properly ordered due to buffering.

LIMITATIONS

  Portability

    Portability is a goal, not a guarantee. "tee" requires fork, except on

    Windows where "system(1, @cmd)" is used instead. Not tested on any

    particularly esoteric platforms yet. See the CPAN Testers Matrix

    <http://matrix.cpantesters.org/?dist=Capture-Tiny> for test result by

    platform.

  PerlIO layers

    Capture::Tiny does its best to preserve PerlIO layers such as ':utf8' or

    ':crlf' when capturing (only for Perl 5.8.1+) . Layers should be applied

    to STDOUT or STDERR *before* the call to "capture" or "tee". This may

    not work for tied filehandles (see below).

  Modifying filehandles before capturing

    Generally speaking, you should do little or no manipulation of the

    standard IO filehandles prior to using Capture::Tiny. In particular,

    closing, reopening, localizing or tying standard filehandles prior to

    capture may cause a variety of unexpected, undesirable and/or unreliable

    behaviors, as described below. Capture::Tiny does its best to compensate

    for these situations, but the results may not be what you desire.

   Closed filehandles

    Capture::Tiny will work even if STDIN, STDOUT or STDERR have been

    previously closed. However, since they will be reopened to capture or

    tee output, any code within the captured block that depends on finding

    them closed will, of course, not find them to be closed. If they started

    closed, Capture::Tiny will close them again when the capture block

    finishes.

    Note that this reopening will happen even for STDIN or a filehandle not

    being captured to ensure that the filehandle used for capture is not

    opened to file descriptor 0, as this causes problems on various

    platforms.

    Prior to Perl 5.12, closed STDIN combined with PERL_UNICODE=D leaks

    filehandles and also breaks tee() for undiagnosed reasons. So don't do

    that.

   Localized filehandles

    If code localizes any of Perl's standard filehandles before capturing,

    the capture will affect the localized filehandles and not the original

    ones. External system calls are not affected by localizing a filehandle

    in Perl and will continue to send output to the original filehandles

    (which will thus not be captured).

   Scalar filehandles

    If STDOUT or STDERR are reopened to scalar filehandles prior to the call

    to "capture" or "tee", then Capture::Tiny will override the output

    filehandle for the duration of the "capture" or "tee" call and then, for

    "tee", send captured output to the output filehandle after the capture

    is complete. (Requires Perl 5.8)

    Capture::Tiny attempts to preserve the semantics of STDIN opened to a

    scalar reference, but note that external processes will not be able to

    read from such a handle. Capture::Tiny tries to ensure that external

    processes will read from the null device instead, but this is not

    guaranteed.

   Tied output filehandles

    If STDOUT or STDERR are tied prior to the call to "capture" or "tee",

    then Capture::Tiny will attempt to override the tie for the duration of

    the "capture" or "tee" call and then send captured output to the tied

    filehandle after the capture is complete. (Requires Perl 5.8)

    Capture::Tiny may not succeed resending UTF-8 encoded data to a tied

    STDOUT or STDERR filehandle. Characters may appear as bytes. If the tied

    filehandle is based on Tie::StdHandle, then Capture::Tiny will attempt

    to determine appropriate layers like ":utf8" from the underlying

    filehandle and do the right thing.

   Tied input filehandle

    Capture::Tiny attempts to preserve the semantics of tied STDIN, but this

    requires Perl 5.8 and is not entirely predictable. External processes

    will not be able to read from such a handle.

    Unless having STDIN tied is crucial, it may be safest to localize STDIN

    when capturing:

      my ($out, $err) = do { local *STDIN; capture { ... } };

  Modifying filehandles during a capture

    Attempting to modify STDIN, STDOUT or STDERR *during* "capture" or "tee"

    is almost certainly going to cause problems. Don't do that.

   Forking inside a capture

    Forks aren't portable. The behavior of filehandles during a fork is even

    less so. If Capture::Tiny detects that a fork has occurred within a

    capture, it will shortcut in the child process and return empty strings

    for captures. Other problems may occur in the child or parent, as well.

    Forking in a capture block is not recommended.

   Using threads

    Filehandles are global. Mixing up I/O and captures in different threads

    without coordination is going to cause problems. Besides, threads are

    officially discouraged.

   Dropping privileges during a capture

    If you drop privileges during a capture, temporary files created to

    facilitate the capture may not be cleaned up afterwards.

  No support for Perl 5.8.0

    It's just too buggy when it comes to layers and UTF-8. Perl 5.8.1 or

    later is recommended.

  Limited support for Perl 5.6

    Perl 5.6 predates PerlIO. UTF-8 data may not be captured correctly.

ENVIRONMENT

  PERL_CAPTURE_TINY_TIMEOUT

    Capture::Tiny uses subprocesses internally for "tee". By default,

    Capture::Tiny will timeout with an error if such subprocesses are not

    ready to receive data within 30 seconds (or whatever is the value of

    $Capture::Tiny::TIMEOUT). An alternate timeout may be specified by

    setting the "PERL_CAPTURE_TINY_TIMEOUT" environment variable. Setting it

    to zero will disable timeouts. NOTE, this does not timeout the code

    reference being captured -- this only prevents Capture::Tiny itself from

    hanging your process waiting for its child processes to be ready to

    proceed.

SEE ALSO

    This module was inspired by IO::CaptureOutput, which provides similar

    functionality without the ability to tee output and with more

    complicated code and API. IO::CaptureOutput does not handle layers or

    most of the unusual cases described in the "Limitations" section and I

    no longer recommend it.

    There are many other CPAN modules that provide some sort of output

    capture, albeit with various limitations that make them appropriate only

    in particular circumstances. I'm probably missing some. The long list is

    provided to show why I felt Capture::Tiny was necessary.

    *   IO::Capture

    *   IO::Capture::Extended

    *   IO::CaptureOutput

    *   IPC::Capture

    *   IPC::Cmd

    *   IPC::Open2

    *   IPC::Open3

    *   IPC::Open3::Simple

    *   IPC::Open3::Utils

    *   IPC::Run

    *   IPC::Run::SafeHandles

    *   IPC::Run::Simple

    *   IPC::Run3

    *   IPC::System::Simple

    *   Tee

    *   IO::Tee

    *   File::Tee

    *   Filter::Handle

    *   Tie::STDERR

    *   Tie::STDOUT

    *   Test::Output

SUPPORT

  Bugs / Feature Requests

    Please report any bugs or feature requests through the issue tracker at

    <https://github.com/dagolden/Capture-Tiny/issues>. You will be notified

    automatically of any progress on your issue.

  Source Code

    This is open source software. The code repository is available for

    public review and contribution under the terms of the license.

    <https://github.com/dagolden/Capture-Tiny>

      git clone https://github.com/dagolden/Capture-Tiny.git

AUTHOR

    David Golden <dagolden@cpan.org>

CONTRIBUTORS

    *   Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>

    *   David E. Wheeler <david@justatheory.com>

    *   fecundf <not.com+github@gmail.com>

    *   Graham Knop <haarg@haarg.org>

    *   Peter Rabbitson <ribasushi@cpan.org>

COPYRIGHT AND LICENSE

    This software is Copyright (c) 2009 by David Golden.

    This is free software, licensed under:

      The Apache License, Version 2.0, January 2004